Lichens and higher plants on stone: a review - AseanBiodiversity.info

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Fig. 6. The stages of a second mode of wall colonization. A moss spore (a) falls on porous stone, such as travertine, <strong>and</strong> develops (b). Atmospheric dust collects on the moss (c) forming a small amount of substrate (d). A seed falls on the substrate (e), germinates (f), grows (g) <strong>and</strong> owers (h). The moss does not damage the substrate but the plant roots penetrate it. Irrespective of the age or historical interest of the building, <strong>plants</strong> that grow in walls have anatomical <strong>and</strong> physiological characteristics that enable them to survive in a dry, inhospitable environment with little soil. These characteristics include: 1. Seeds that can reach cracks or small cavities in the building material. The main agents of dispersal that can achieve this are wind (for light seeds produced in large quantity: e.g. of Parietaria di usa, Centranthus ruber), ants (e.g. for Chelidonium majus, Mercurialis annua), <strong>and</strong> birds that eat eshy fruits (e.g. of Ficus carica, Hedera helix). Man can also act as agent in the case of <strong>plants</strong> that “escape” from gardens <strong>and</strong> grow wild in walls (e.g. Antirrhinum majus, Cheiranthus cheiri, Matthiola incana). 2. Seeds that germinate with a minimum of moisture. 3. Early sexual maturity. Arboreal species that grow in walls can be regarded as “natural bonsai”. 4. Vegetative reproduction, permitting the plant to have an alternative method when sexual reproduction fails. 5. Drought resistance. Centranthus ruber, for example, grows on the edge of the crater of Vesuvius <strong>and</strong> in the ruins of Pompei, environments with little water or substrate. 6. Deep rooting <strong>and</strong> capable of growing in rock crevice. The microsites in which these <strong>plants</strong> grow are illustrated in Fig. 7 <strong>and</strong> described below. The positions occupied by <strong>plants</strong> on the ideal ruin hold for any historical building. A. Cavities at ground level. This situation hosts many species since substrate naturally collects there <strong>and</strong> rain water does not run o . The roots of the plant may even penetrate the earth. Plants growing in this situation su er less environmental stress. B. Cavities in inclined surfaces. This situation o ers more possibilities for seeds to lodge <strong>and</strong> for moisture than vertical surfaces. C: Cavities between two types of building material. The greater the chemical di erence between the two materials, the more nutrients are available. D. Cavities in a vertical face of homogeneous material. This situation is the most hostile to plant growth since water is limited to wind-driven rain. E. Cavities in horizontal surfaces. Water availability is good but the plant must be capable of retaining it. F. Cavities at the junction of vertical <strong>and</strong> horizontal surfaces. This situation has similar water availability to A, but there is less substrate. G. Cavities where two vertical surfaces meet. This situation is similar to F but o ers less moisture. H. Substrate formed on a horizontal porous surface.The situation is constituted by a corbel, a decorative element in Roman buildings <strong>and</strong> Baroque <strong>and</strong> Renaissance churches. It is usually made of marble, travertine or s<strong>and</strong>stone.
Fig. 7. The main microsites for plant growth: cavities A, at ground level; B, on inclined surface; C, at junction of two materials; D, in homogeneous vertical face; E, in horizontal surface; F, at junction of vertical <strong>and</strong> horizontal faces; G, at junction of two vertical faces; substrate, H, on horizontal porous surface; I, on ruined stonework; space, J, between wall <strong>and</strong> stone facade. Rhizomes, K, from <strong>plants</strong> growing in soil may invade the wall. Moisture is di erent in eachsituation. Sites B, C <strong>and</strong> D are very dry, receiving only wind-driven rain. Sites A, F <strong>and</strong> G retain some rainwater <strong>and</strong> E, H, I, J <strong>and</strong> K are the wetest because the horizontal substrate absorbs all the rain it receives (modi ed from Lisci <strong>and</strong> Pacini, 1993a). I. Substrate formed on ruined stonework. This is a special situation mainly found in Roman ruins. It results from the destruction of rubble <strong>and</strong> lime mortar- lled walls or pillars. J. Spaces between a wall <strong>and</strong> its stone facade. This situation hosts <strong>plants</strong> with rhizomes, which if vigorous, may detachthe facade. K. Wall invaded by the rhizome of a plant in adjacent soil. This situation occurs with retaining walls <strong>and</strong> has been observed withtrees <strong>and</strong> shrubs suchas Celtis australis, Ailanthus altissima <strong>and</strong> Syringa vulgaris, <strong>and</strong> withrhizomatous <strong>and</strong> stoloniferous herbs. Table 1 lists the most common <strong>plants</strong> <strong>and</strong> the main microsites that they occupy (in terms of Fig. 7). Comparison of Fig. 7 <strong>and</strong> Table 1 reveals that the number of <strong>plants</strong> that grow on buildings is greatest for horizontal surfaces (Fig. 7: E,H,I). This is because these situation o er: (a) better conditions for growth(i.e. more water <strong>and</strong> substrate); (b) more chance of seeds l<strong>and</strong>ing; (c) a good perch for birds that excrete seeds; (d) a good site for ant nests where seeds are stored. The number of <strong>plants</strong> decreases in environments in which there is little precipitation <strong>and</strong> relative humidity is low all year round. The ruins of Roman towns in north Africa (Tunisia <strong>and</strong> Libya) host only drought resistant species. Buildings of historical interest in parts of Asia (Burma, China, India, Indonesia, Thail<strong>and</strong>) <strong>and</strong> America (Mexico, Peru), characterized by high rainfall, develop luxuriant vegetation which is destructive if not controlled.
Page 1 and 2: Abstract Lichens <
Page 3 and 4: Plate 1. (a) Statue in archaeologic
Page 5 and 6: Fig. 3. Di erent structures of vege
Page 7: e avoided on windy days and
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Page 14 and 15: Table 1. Continued Families <strong
Page 16 and 17: Corball, R., Paz-Bermudez, G., Sanc

Lichens and higher plants on stone: a review - AseanBiodiversity.info

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